Several findings were made concerning membrane hydrolysis across permselective porous membranes. The attainment of Donnan equilibria was more readily attained with protamine membranes than with sulfonated polystyrene membranes. One possible cause for this may be the slightly acidic solutions that routinely develop when aqueous solutions are exposed to air. The anticipated elevation of concentration potentials at low electrolyte concentrations was found to be true when the concentration ratio of one of the ions of water was made the same as that of the electrolyte, i.e., the Donna distribution was present. A different type of membrane hydrolysis was shown to occur with a paraffin oil membrane. The mechanism depends upon the selective transport of undissociated electrolytes across the membrane.